Thanks for the replies.
Unfortunately, I had to remove the system from the client site as they could not work with this problem.
Mr X, I did try a support call with Sangoma and spent a few hours talking to them, sending logs & conf files to no avail. They escalated the call and then never got back to me.
My own research turned up the following:
Sangoma NBE passes a number of fields from the ISDN setup message through to the routing rules section, they include dnis and ani (i.e. called and caller numbers)
They also pass the entire ISDN setup message in the field pstn.in.isdn.setup.ie.0xZZ.0xYY
They do NOT pass the ISDN TON (Type Of Numner) field, apart from in hex format in the setup message.
A RegEx Guru, or hopefully Snom ONE expert could write a routing rule to append either a single or double zero the the sip.out.from.uri field depending on the content of the relevant ISDN call setup message.
You already have a pstn.out.ani.type, so why not include a pstn.in.uri.type?
Fair enough if this is a Sangoma problem, I'll speak to them (again). My main concern is that I'm about to purchase a Snom ONE Plus T1/E1/J1 and want to avoid the same problem.
Does anyone know if the Snom ONE Plus uses Net Border Express or does it have its own ISDN gateway/interface software?